This invention relates in general to a vehicular drive train assembly including a source of rotational power and a multiple speed axle for providing a desired speed reduction gear ratio between the source of rotational power and the driven wheels of the vehicle. More particularly, this invention relates to a method for automatically controlling the operation of the multiple speed axle assembly in such a vehicle drive train assembly.
In virtually all land vehicles in use today, a drive train assembly is provided including a source of rotational power and a driven axle having rotatably driven wheels. In many instances, the source of rotational power is embodied as an internal combustion or diesel engine. Such engines are designed to operate within a relatively narrow range of speeds and are not well adapted for operation at very low or very high speeds. Thus, the drive train assembly of an engine driven vehicle typically includes a coupling mechanism connected to the engine and a transmission connected between the coupling mechanism and the driven axle. The coupling mechanism is provided to selectively disconnect the engine from driving the remaining components of the drive train assembly, allowing the engine to run while the vehicle is stopped. The transmission provides a plurality of speed reduction gear ratios between the engine and the driven axle, thereby facilitating the smooth acceleration and deceleration of the vehicle.
The operations of the coupling mechanism and the transmission are often accomplished manually, i.e., in response to physical effort by the driver of the vehicle. In such a manually operated system, the coupling mechanism is usually embodied as a mechanical clutch. When the clutch is engaged, the transmission is driven by the vehicle engine to operate the vehicle at the selected gear ratio. To shift the transmission from a first gear ratio to a second gear ratio, the clutch is initially disengaged such that power is not transmitted from the vehicle engine to the transmission. This allows the gear shifting operation to occur within the transmission under a non-torque loading condition to prevent undesirable clashing of the meshing gear teeth. Thereafter, the clutch is re-engaged such that power is transmitted from the vehicle engine to the transmission to operate the vehicle at the second gear ratio.
A typical structure for a mechanical clutch includes a cover that is connected to a flywheel secured to the end of the output shaft of the vehicle engine for rotation therewith. A pressure plate is disposed within the clutch between the cover and the flywheel. The pressure plate is connected for rotation with the flywheel and the cover, but is permitted to move axially relative thereto. Thus, the flywheel, the cover, and the pressure plate are all constantly rotatably driven by the vehicle engine. Between the flywheel and the pressure plate, a driven disc assembly is disposed. The driven disc assembly is supported on the transmission input shaft for rotation therewith, but is permitted to move axially relative thereto. To engage the clutch, the pressure plate is moved axially toward the flywheel to an engaged position, wherein the driven disc assembly is frictionally engaged between the flywheel and the pressure plate. As a result, the driven disc assembly (and the transmission input shaft upon which it is supported) are driven to rotate with the flywheel, the cover, and the pressure plate. To disengage the clutch, the pressure plate is moved axially away from the flywheel to a disengaged position. When the pressure plate is moved axially to this disengaged position, the driven disc assembly is not frictionally engaged between the flywheel and the pressure plate. As a result, the driven disc assembly (and the transmission input shaft upon which it is supported) are not driven to rotate with the flywheel, the cover, and the pressure plate.
To effect such axial movement of the pressure plate between the engaged and disengaged positions, most mechanical clutches are provided with a release assembly including a generally hollow cylindrical release sleeve which is disposed about the transmission input shaft. The forward end of the release sleeve extends within the clutch and is connected through a plurality of levers or other mechanical mechanism to the pressure plate. In this manner, axial movement of the release sleeve causes corresponding axial movement of the pressure plate between the engaged and disengaged positions. Usually, one or more engagement springs are provided within the clutch to urge the pressure plate toward the engaged position. The engagement springs typically react between the release sleeve and the cover to normally maintain the clutch in the engaged condition. The rearward end of the release sleeve extends outwardly from the clutch through a central opening formed through the cover. Because the release sleeve is connected to the cover and the pressure plate of the clutch, it is also constantly driven to rotate whenever the vehicle engine is operating. Thus, an annular release bearing is usually mounted on the rearward end of the release sleeve. The release bearing is axially fixed on the release sleeve and includes an inner race which rotates with release sleeve, an outer race which is restrained from rotation, and a plurality of bearings disposed between the inner race and the outer race to accommodate such relative rotation. The non-rotating outer race of the release bearing is typically engaged by an actuating mechanism for moving the release sleeve (and, therefore, the pressure plate) between the engaged and disengaged positions to operate the clutch. The clutch can be disengaged by depressing a clutch pedal located in the driver compartment of the vehicle. The clutch pedal is connected through a mechanical linkage to the outer race of the release bearing of the clutch such that when the clutch pedal is depressed, the pressure plate of the clutch is moved from the engaged position to the disengaged position. When the clutch pedal is released, the engagement springs provided within the clutch return the pressure plate from the disengaged position to the engaged position.
A typical structure for the manual transmission includes a case containing a transmission input shaft connected to the source of rotational power, a transmission output shaft connected to the driven axle, and a plurality of meshing gears. A manually operable structure is provided for connecting selected ones of the meshing gears between the transmission input shaft and the transmission output shaft to provide a desired speed reduction gear ratio therebetween. The meshing gears contained within the transmission case are of varying size so as to provide a plurality of such gear ratios. By appropriately shifting among these various gear ratios, acceleration and deceleration of the vehicle can be accomplished in a smooth and efficient manner. The gear shifting operation in the transmission can be performed when the clutch is disengaged by manually moving a shift lever which extends from the transmission into the driver compartment of the vehicle. Manually operated clutch and transmission assemblies of this general type are well known in the art and are relatively simple, inexpensive, and lightweight in structure and operation. Because of this, the majority of medium and heavy duty truck clutch/transmission assemblies in common use today are manually operated.
The operations of the coupling mechanism and transmission may also be accomplished automatically, i.e., without any physical effort by the driver of the vehicle. In order to improve the convenience of use of manually operated clutch/transmission assemblies described above, various structures have been proposed for partially or fully automating the shifting of an otherwise manually operated transmission. In a partially or fully automated manual transmission, the driver-manipulated clutch pedal may be replaced by an automated clutch actuator, such as a hydraulic or pneumatic actuator. The operation of the automated clutch actuator can be controlled by an electronic controller or other control mechanism to selectively engage and disengage the clutch without manual effort by the driver. Similarly, the driver-manipulated shift lever may also be replaced by an automated transmission actuator, such as a hydraulic or pneumatic actuator which is controlled by an electronic controller or other control mechanism to select and engage desired gear ratios for use.
The driven axle assemblies are provided to transmit the rotational power to the driven wheels of the vehicle. A typical axle assembly includes a housing containing an axle input shaft that is connected through a differential gear assembly to a pair of axle output shafts. The differential gear assembly splits the rotational power from the axle input shaft to the two axle output shafts and, therefore, rotatably drives the wheels of the vehicle. In some instances, the axle assembly is structured to provide only a single speed reduction gear ratio between the axle input shaft to the axle output shafts. In other instances, however, the axle assembly is structured to provide two (or possibly more) speed reduction gear ratios between the axle input shaft to the axle output shafts. Multiple speed axle assemblies are desirable because they extend the number of speed reduction gear ratios beyond those provided by the transmission in a relatively simple and cost efficient manner. For example, a four-speed transmission that is operated in conjunction with a two-speed axle assembly provides a total of eight available gear ratios.
In these multiple speed axle assemblies, it is known to provide a manually operable mechanism for shifting among the axle gear ratios. In the past, this manually operable mechanism included a mechanical linkage extending from the driver compartment of the vehicle to the axle assembly. The driver of the vehicle physically moved the mechanical linkage to shift among the axle gear ratios. More recently, however, this manually operable mechanism included an electrical switch connected to operate an electric motor provided on the axle assembly. The driver of the vehicle manually operated the electrical switch to control the operation of the electric motor to shift among the axle gear ratios.
It is well known to manually operate a multiple speed axle assembly in conjunction with a manual clutch/transmission assembly. However, a manually operable multiple speed axle assembly cannot readily be used with a partially or fully automated manual transmission or with an automatic transmission as described above. Furthermore, a manually operable multiple speed axle assembly cannot readily be used with a variable speed motor that is directly connected thereto. Thus, it would be desirable to provide a controller for automatically controlling the operation of a multiple speed axle assembly with either a partially or fully automated manual transmission, an automatic transmission, or a variable speed motor in a vehicle drive train assembly.